Reproducibility of phase formation has been an important issue in tailoring electronic and thermal transport properties of NaxCoO2-based thermoelectric materials; however, optimized synthesis conditions for single phase of polycrystalline NaxCoO2 remain unsatisfactory. Here, we show that phase formation of a Na-Co-O-based system can be controlled by adjusting the reaction temperature. Single phase of Na0.75CoO2 was fabricated by optimized heat treatment for both suppression of Na2O vaporization and CoO phase formation. The largest thermoelectric power factor of the present compound (∼5.4 × 10−4 W/mK2 at 973 K) is comparable to that of reported values for single phase polycrystalline NaxCoO2 bulks. In addition, Na0.75CoO2 phase obtained by this approach was confirmed to be stable at high temperatures up to 1000 K.
Bibliographical noteFunding Information:
This work was supported by a Fundamental Research and Development Program for Core Technology of Materials Grant funded by the Ministry of Trade, Industry and Energy, Republic of Korea (10048035). This work was also supported by a research program funded by Koreatech.
© 2014, The Minerals, Metals & Materials Society.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry